Topological weak containment

Abstract

We build on work of Elek and Zucker and develop a topological analogue of the theory of weak containment. We show that definitions in terms of local patterns, containment in ultra(co)products, and continuous model theory are all equivalent, just as in ergodic theory. And, for actions on Cantor space, we show these are all equivalent to approximate conjugacy. Restricting our attention to Cantor space, we connect this theory to questions about generic actions. We show how the shape of the space of weak equivalence classes reflects the geometry of the acting group. And, we show that, for $\mathbb{Z}^2$, there is no smallest limit of finite actions.